/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
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 *
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 *
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 *
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 *
 *
 *
 *
 *
 *
 *
 */

package java.util.zip;

import java.nio.ByteBuffer;
import sun.nio.ch.DirectBuffer;

/**
 * A class that can be used to compute the CRC-32 of a data stream.
 *
 * <p> Passing a {@code null} argument to a method in this class will cause
 * a {@link NullPointerException} to be thrown.
 *
 * @author David Connelly
 * @see Checksum
 */
public class CRC32 implements Checksum {

  private int crc;

  /**
   * Creates a new CRC32 object.
   */
  public CRC32() {
  }


  /**
   * Updates the CRC-32 checksum with the specified byte (the low
   * eight bits of the argument b).
   *
   * @param b the byte to update the checksum with
   */
  public void update(int b) {
    crc = update(crc, b);
  }

  /**
   * Updates the CRC-32 checksum with the specified array of bytes.
   *
   * @throws ArrayIndexOutOfBoundsException if {@code off} is negative, or {@code len} is negative,
   * or {@code off+len} is greater than the length of the array {@code b}
   */
  public void update(byte[] b, int off, int len) {
    if (b == null) {
      throw new NullPointerException();
    }
    if (off < 0 || len < 0 || off > b.length - len) {
      throw new ArrayIndexOutOfBoundsException();
    }
    crc = updateBytes(crc, b, off, len);
  }

  /**
   * Updates the CRC-32 checksum with the specified array of bytes.
   *
   * @param b the array of bytes to update the checksum with
   */
  public void update(byte[] b) {
    crc = updateBytes(crc, b, 0, b.length);
  }

  /**
   * Updates the checksum with the bytes from the specified buffer.
   *
   * The checksum is updated using
   * buffer.{@link java.nio.Buffer#remaining() remaining()}
   * bytes starting at
   * buffer.{@link java.nio.Buffer#position() position()}
   * Upon return, the buffer's position will
   * be updated to its limit; its limit will not have been changed.
   *
   * @param buffer the ByteBuffer to update the checksum with
   * @since 1.8
   */
  public void update(ByteBuffer buffer) {
    int pos = buffer.position();
    int limit = buffer.limit();
    assert (pos <= limit);
    int rem = limit - pos;
    if (rem <= 0) {
      return;
    }
    if (buffer instanceof DirectBuffer) {
      crc = updateByteBuffer(crc, ((DirectBuffer) buffer).address(), pos, rem);
    } else if (buffer.hasArray()) {
      crc = updateBytes(crc, buffer.array(), pos + buffer.arrayOffset(), rem);
    } else {
      byte[] b = new byte[rem];
      buffer.get(b);
      crc = updateBytes(crc, b, 0, b.length);
    }
    buffer.position(limit);
  }

  /**
   * Resets CRC-32 to initial value.
   */
  public void reset() {
    crc = 0;
  }

  /**
   * Returns CRC-32 value.
   */
  public long getValue() {
    return (long) crc & 0xffffffffL;
  }

  private native static int update(int crc, int b);

  private native static int updateBytes(int crc, byte[] b, int off, int len);

  private native static int updateByteBuffer(int adler, long addr,
      int off, int len);
}
